This invention relates to the laser printing of stereoscopic, multiple images or motion images which will be used in conjunction with a lenticular element.
Lenticular arrays or overlays are a known means to give images the appearance of depth or motion. A lenticular image is created using a transparent upper layer having narrow parallel lenticules (half cylindrical lenses) on the outer surface and an image containing substrate or lower layer which projects images through the lenticules. The two layers form a lenticular system wherein each image is selectively visible as a function of the angle from which the system is viewed. A depth image is a composite picture made by bringing together into a single composition a number of different parts of a scene viewed from different angles. When the lenticules are vertically oriented, each eye of a viewer will see different elements and the viewer will interpret the net result as depth of field. The viewer may also move his head with respect to the image thereby observing other views with each eye and enhancing the sense of depth. Each lenticule is associated with a plurality of image lines or an image line set and the viewer is supposed to see only one image line (or view slice) of each set with each eye for each lenticule. It is imperative that the line image sets be registered accurately with the lenticules, so that the proper picture is formed when the assembly is viewed.
This process can be used to generate a three-dimensional effect at a proper viewing distance or multiple images by viewing from different angles. When the lenticules are oriented horizontally, each eye receives the same image. In this case, the multiple images upon moving the lenticular can be used to generate the illusion of motion. For whichever orientation the lenticules are oriented, each of the viewed images is generated by lines from an image which has been interlaced substantially at the frequency of the lenticular array, number of lenticules per length and with the desired number of images.
One method of recording of linear images on a lenticular recording material is accomplished with a stereoscopic image recording apparatus (hereunder referred to simply as xe2x80x9ca recording apparatusxe2x80x9d) that relies upon optical exposure (printing). With this recording apparatus, original transmission images are projected from a light source. The light transmitted through the original images passes through the projection lenses of the recording apparatus to be focused on the lenticular recording material via a lenticular sheet. The original images are thereby exposed as linear images.
Another method of image recording uses scanning exposure which requires comparatively simple optics and yet has great flexibility in adapting to various image-processing operations and to alterations in the specifications of the lenticular sheet.
In the article entitled xe2x80x9cDevelopment of Motion Image Printerxe2x80x9d, by H. Akahori et al., ISandT 50th Annual Conference Proceedings, page 305, there is a disclosure of a printer for printing stereoscopic images using a thermal head and thermal dye transfer in registration with the lenticular material. The receiver sheet must be heated to achieve the necessary stability for registration of the images with the lenticular material. The resolution is six images on 100 DPI lenticular material with a 300 DPI thermal head. However, there is a problem with this method in that low resolution images are obtained, since heat transferred from the resistive head xe2x80x9cspreadsxe2x80x9d through the support during printing.
EP 0 596 629A2 and EP 0 659 026A2 disclose a method and apparatus for directly printing on lenticular supports using lasers. This method generates an image in contact with the lenticular material. There is a problem with this method, however, in that the dyes can continue to migrate after transfer, resulting in unacceptable image ghosting (adjacent views bleeding through).
An object of this invention is to generate high resolution lenticular images which are resistant to thermal dye diffusion. It is another object of this invention to generate images efficiently with high abrasion resistance.
These and other objects are achieved in accordance with this invention which relates to a diffusion resistant lenticular element comprising a support having a lenticular array thereon, the element having thereon an acidic mordanting layer containing a laser-induced, cationic dye image, the mordanting layer being on the side of the support which does not contain the lenticular array.
Another embodiment of the invention relates to a process of forming a diffusion resistant lenticular element comprising:
a) contacting at least one dye-donor element comprising a support having thereon a dye layer comprising an image dye in a binder having an infrared-absorbing material associated therewith, the image dye comprising a nonionic dye capable of being converted to a cationic dye by means of an acid, with a lenticular element comprising a support having a lenticular array thereon on the opposite side thereof;
b) imagewise-heating the dye-donor element by means of a laser;
c) transferring a dye image to the support of the lenticular element;
d) contacting the dye image with an acidic mordanting layer; and
e) heating the element to cause the nonionic dye to convert to a cationic dye which is mordanted in the acidic mordanting layer.
By use of the invention, a high resolution lenticular image is generated efficiently which is resistant to thermal dye diffusion and has a high abrasion resistance.
As noted above, dyes useful in the invention are nonionic dyes capable of being converted to cationic dyes by means of an acid. A cationic dye diffuses much less readily than a nonionic dye due to electrostatic forces retarding movement. An example of an nonionic dye which converts to a cationic dye in the presence of an acid is the following (Since the chromophore is involved in the reaction, there is a color change indicating the state of the dye molecule): 
Examples of such dyes which may be used in the invention are of many classes. For example, the dye may be a deprotonated cationic dye which is capable of being reprotonated to a cationic dye having an Nxe2x80x94H group which is part of a conjugated system. Additional examples of such dyes are disclosed in U.S. Pat. No. 5,523,274, the disclosure of which is hereby incorporated by reference, and include the following: 
Another class of dyes useful in the invention is a pendant basic dye capable of being protonated to a cationic dye, as disclosed in U.S. Pat. Nos. 5,512,532, 5,744,422, and 5,804,531, the disclosures of which are hereby incorporated by reference. An example of a pendant basic dye which converts to a cationic dye in the presence of an acid is the following: 
Additional examples of such dyes include the following: 
Another class of dyes useful in the invention is a lactone leuco dye capable of being protonated to a cationic dye, as disclosed in U.S. Pat. No. 5,830,823 and copending U.S. Ser. No. 08/996,388, the disclosures of which are hereby incorporated by reference. An example of a lactone leuco dye which converts to a cationic dye in the presence of an acid is the following: 
An additional example of such dyes includes the following: 
Another class of dyes useful in the invention is a carbinol dye capable of being protonated to a cationic dye, as disclosed in U.S. Pat. No. 5,804,531, the disclosure of which is hereby incorporated by reference. An example of a carbinol dye which converts to a cationic dye in the presence of an acid is the following: 
The mordanting layer useful in the invention is acidic, which may be the result of adding an acid to a polymer or using an acidic polymer. In a preferred embodiment of the invention, an acidic polymer is used such as described in U.S. Pat. No. 5,523,274, the disclosure of which is hereby incorporated by reference. Examples of such polymers include condensation polymers such as polyesters, polyurethanes, polycarbonates, etc.; addition polymers such as polystyrenes, vinyl polymers, etc.; block copolymers containing large segments of more than one type of polymer covalently linked together; provided such polymeric material contains acid groups as part of the polymer chain. In a preferred embodiment of the invention, the mordanting layer comprises an acrylic polymer, a styrene polymer or a phenolic resin.
The dyes of the dye-donor element used in the invention can optionally be dispersed in a polymeric binder such as a cellulose derivative, e.g., cellulose acetate hydrogen phthalate, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose triacetate or any of the materials described in U.S. Pat. No. 4,700,207; polyvinyl butyrate; copolymers of maleic anhydride with vinyl ethers such as methyl vinyl ether; polycyanoacrylates; a polycarbonate; poly(vinyl acetate); poly(styrene-co-acrylonitrile); a polysulfone or a poly(phenylene oxide), gelatin, etc. The binder may be used at a coverage of from about 0.1 to about 5 g/m2.
Any material can be used as the support for the lenticular array of the invention provided it is dimensionally stable. Such materials include polyesters such as poly(ethylene terephthalate); polyamides; polycarbonates; cellulose esters such as cellulose acetate; fluorine polymers such as poly(vinylidene fluoride) or poly(tetrafluoroethylene-co-hexafluoropropylene); polyethers such as polyoxymethylene; polyacetals; polyolefins such as polystyrene, polyethylene, polypropylene or methylpentene polymers; and polyimides such as polyimide-amides and polyether-imides. The support generally has a thickness of from about 50 to about 5000 xcexcm. While the lenticular array may be provided on a separate support, generally the support and the array are in one integral element.
Infrared-absorbing materials which may be used in the invention include carbon black, cyanine infrared-absorbing dyes as described in U.S. Pat. No. 4,973,572, or other materials as described in the following U.S. Pat. Nos. 4,948,777; 4,950,640; 4,950,639; 4,948,776; 4,948,778; 4,942,141; 4,952,552; 5,036,040; and 4,912,083, the disclosures of which are hereby incorporated by reference.
A laser is used to transfer dye from the dye-donor element used in the invention. It is preferred to use a diode laser since it offers substantial advantages in terms of its small size, low cost, stability, reliability, ruggedness, and ease of modulation.
Lasers which can be used to transfer dye from dye-donors employed in the invention are available commercially. There can be employed, for example, Laser Model SDL-2420-H2 from Spectra Diode Labs, or Laser Model SLD 304 V/W from Sony Corp.
A thermal printer which uses the laser described above to form an image on a thermal print medium is described and claimed in U.S. Pat. No. 5,268,708, the disclosure of which is hereby incorporated by reference.
Spacer beads may be employed in a separate layer over the dye layer of the dye-donor element in the above-described laser process in order to separate the donor from the receiver during dye transfer, thereby increasing the uniformity and density of the transferred image. That invention is more fully described in U.S. Pat. No. 4,772,582, the disclosure of which is hereby incorporated by reference. Alternatively, spacer beads may be employed in the receiving layer of the receiver as described in U.S. Pat. No. 4,876,235, the disclosure of which is hereby incorporated by reference. The spacer beads may be coated with a polymeric binder if desired.
As noted above, in the process of the invention, the lenticular element with the transferred dye is heated to cause the nonionic dye to convert to a cationic dye which is mordanted in the adhesive layer. This heating may be accomplished, for example bypassing the element between a pair of heated rollers. Other methods of heating could also be used such as using a heated platen, use of pressure and heat, external heating, etc. Mechanical adhesion may be used to maintain registration after heating and mordanting if sufficient adhesion does not occur between the acidic mordanting layer and the lenticular array element. The mechanical adhesion, for example, can be in the form of clamps, registration pins or a frame.